61.

The number of α-particles and β-particles respectively emitted in the reaction  ₈₈A¹⁹⁶  →  ₇₈B¹⁶⁴ are

• 8 and 8

• 8 and 6

• 6 and 8

• 6 and 6

The counting rate observed from a radioactive source at t = 0 s was 1600 count/s and at t = 8 s it was 100 counts/s. The counting rate observed as counts per second at t = 6 s, will be

• 400

• 300

• 250

• 200

C¹⁴ has half-life 5700 year. At the end of 11400 years, the actual amount left is

• 0.5 of original amount

• 0.25 of original amount

• 0.125 of original amount

• 0.0625 of original amount

Li nucleus has three protons and four neutrons. Mass of lithium nucleus is 7.016005 amu. Mass of proton is 1.007277 amu and mass of neutron is 1.008665 amu. Mass defect for lithium nucleus in amu is

• 0.04048 amu

• 0.04050 amu

• 0.04052 amu

• 0.04055 amu

Two radioactive nuclides x and y have half-lives 1 h and 2 h respectively. Initially the samples have equal number of nuclei. After 4 h the ratio of the numbers of x and y is

• $\frac{1}{2}$

• 2

• $\frac{1}{4}$

• 1

₉₂U²³⁸ decays successively to form ₉₀Th²³⁴, ₉₁Pa²³⁴, ₉₂U²³⁴, ₉₀Th²³⁰, ₈₈Ra²²⁶ then during the reaction the number of α-particles emitted is

• 4

• 3

• 5

• 2

Half-life of a radioactive substance is 20 minutes. The time between 20% and 80% decay will be

• 40 minutes

• 20 minutes

• 25 minutes

• 30 minutes

A hypothetical radioactive nucleus decays according to the following series.

${}_{72}{\mathrm{A}}^{180} \stackrel{\mathrm{\alpha }}{\to } {\mathrm{A}}_1 \stackrel{{\mathrm{\beta }}^{-}}{\to } {\mathrm{A}}_2 \stackrel{\mathrm{\alpha }}{\to } {\mathrm{A}}_3 \stackrel{\mathrm{\gamma }}{\to } {\mathrm{A}}_4$

If the mass number and atomic number of A are respectively 180 and 72. Then the atomic number and mass number of A will respectively be

• 69, 171

• 70, 172

• 68, 172

• 69, 172

Nucleus A is converted into C through the following reactions

         $$\begin{gathered} \mathrm{A} \underset{}{\to } \mathrm{B} + \mathrm{\alpha } [\mathrm{\alpha } - \mathrm{alpha} \mathrm{paricle}] \\ \mathrm{B} \underset{}{\to } \mathrm{C} + 2\mathrm{\beta } [\mathrm{\beta }-\mathrm{electron}], \mathrm{then} \end{gathered}$$

• A and B are isotopes

• A and C are isobars

• A and B are isobars

• A and C are isotopes

If m, m_n , and m_p are the masses of _ZX^A nucleus, neutron and proton respectively

• m = (A − Z)m_n + Zm_p

• m < (A − Z)m_n + Zm_p

• m > (A − Z)m_n + Zm_p

• m = (A − Z)m_p + Zm_n